| 摘要 |
PROBLEM TO BE SOLVED: To provide a radio direction finder whose detecting capacity can be enhanced reasonably. SOLUTION: In the radio direction finder 500, the arrival direction D1 of radio waves at a detecting frequency Fd is displayed on the basis of received signals received by a plurality of antenna elements 110c projected to the vertical direction from support arm bodies 125 projected to the horizontal direction. One or both of the length L21 of every antenna element 110c and the length L31 up to the position of every antenna element 110c from the center of a center holding body 130 are expanded and contracted by a drive mechanism 430. The drive mechanism 430 makes the lengths L21, L31 correspond to the detecting frequency Fd, or it, is driven by an electric motor or manually in such a way that the lengths correspond stepwise to the detecting frequency Fd. The drive mechanism 430 is constituted of one or a plurality of rope mechanisms timing belt mechanisms, chain mechanisms or cam mechanisms. When the frequency band of the detecting frequency is wide, a plurality of similar antenna devices 100 are arranged.
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